1. Field of the Invention
The present invention relates to a communication apparatus and a communication method and more particularly to a communication apparatus and a communication method that allow a plurality of communicating parties to be individually identified with accuracy so as to prevent responses from being simultaneously received from two or more communicating parties in, for example, near field communication or the like.
2. Description of the Related Art
As a system used for the near field communication, an integrated circuit (IC) system, for example, is widely known. In an IC card system, a reader/writer generates electromagnetic waves to form a so-called radio frequency (RF) field or a magnetic field. When an IC card is brought close to the reader/writer, power is supplied to the IC card by electromagnetic induction and data is transferred to and from the reader/writer.
The IC card systems currently available come in, for example, type A, type B and type C.
Type A adopts the Philips' MIFARE system. Data encoding by Miller is performed for the transmission of data from a reader/writer to an IC card, while data encoding by Manchester is performed for the transmission of data from the IC card to the reader/writer. Type A uses a data transmission rate of 106 kbps (kilo bits per second).
In Type B, data encoding based on NRZ is performed for the transmission of data from a reader/writer to an IC card, while data encoding based on NRZ-L is performed for the transmission of data from the IC card to the reader/writer. Type B uses a data transmission rate of 106 kbps.
Type C is based on the FeliCa technology developed by Sony Corporation, which is the assignee of the present application. Data encoding by Manchester is performed for the transmission of data between a reader/writer and an IC card. Type C uses a data transmission rate of 212 kbps (kilo bits per second).
In an IC card system, when a plurality of IC cards are brought closely to a single reader/writer, the reader/writer is required to identify each of the IC cards so as to identify each communicating party when performing communication.
A method is available for identifying a plurality of IC cards by assigning unique identification numbers (hereinafter referred to as IDs) to the IC cards and have the IDs reported from the IC cards to the reader/writer.
If unique IDs are assigned to the IC cards, as in the case described above, then the IDs will not be overlapped among IC cards. In this case, however, memories, such as electrically erasable programmable read only memories (EEPROMs), are required to always store the unique IDs. This means that the IC cards must be provided with EEPROMs to store their IDs even when the EEPROMs are not necessary, disadvantageously resulting in higher manufacturing cost.
As a solution to the above problem, a method is available in which random numbers are generated in the IC cards and the generated random numbers are temporarily used as their IDs. This method obviates the need for always storing the IDs and therefore obviates the need for providing them with the EEPROMs for storing IDs.
However, if random numbers are used for the IDs, then the same random numbers may be used as the IDs by a plurality of IC cards. If this happens, when a reader/writer transmits data on the basis of the ID, a plurality of IC cards simultaneously responds, causing a collision to take place. This prevents the reader/writer from properly receiving the responses from the IC cards.